A crucial part of stable management is equine nutrition, but one of the primary nutrients, protein, is often misunderstood. By applying some research­-based principles you can establish the correct level of protein you feed different horses.

Protein: the Background

Horses vary in their protein requirement, by age and lifestyle. For example, because protein is the primary structural nutrient needed for building bone, muscle and most body tissues, growing horses and lactating broodmares need to consume elevated levels of high quality protein. Most foal and broodmare concentrates will be 14 to 16 percent protein. Similarly, older horses (20 + years) can benefit from more protein. For this reason, most senior rations are 14 percent protein.

For many years horsemen assumed working horses also needed more protein. During work, however, the horse will first burn carbohydrates (sugar) then fat and lastly body protein. The fact is that hard work only slightly increases the horse’s need for additional protein and as we feed more pounds of grain to meet its caloric needs, we naturally satisfy the animal’s protein requirements. If any legume (alfalfa or clover) forages are being consumed, the adult horse doesn’t need any more than 10 percent protein in the grain concentrate. If very poor quality grass hay is being fed, a 12 percent protein grain concentrate may help. The exception to this rule is the aged horse which needs more.

Not all protein is created equal. The building blocks of protein are amino acids. Some amino acids must be in the horse’s diet, while other amino acids can be synthesized by the horse’s hindgut bacteria and liver. Amino acids that must be included in the ration are called essential or limiting amino acids. If they are not fed in sufficient quantities, a horse’s growth and performance are limited.

Examples of essential amino acids are lysine and methionine. Lysine is critical for most body tissues, and methionine is a required component of hoof and hair. Higher quality grain rations will include added lysine and methionine. In fact, some feed companies now guarantee the presence of these two amino acids.

What Protein Does Do

Overfeeding protein causes an excess that will escape digestion in the small intestine and be converted to ammonia by the bacteria in the horse’s hindgut. Ammonia is a very toxic chemical, and its existence in the hindgut will alter the horse’s acid-base (pH) balance and upset bacteria fermentation. Ammonia will also hamper muscle metabolism and depress the immune system.

Another problem with excess ammonia, in some parts of the country, is colic caused by intestinal stones (enteroliths). Why the stones form is not completely understood. However, it has been determined that farms feeding rich high-protein alfalfa put their horses at risk. The excess protein and resultant ammonia production are thought to lower the colon’s pH so that minerals precipitate into stones. If alfalfa is fed, avoid a grain concentrate high in protein.

Still another hazard of excess ammonia is its absorption into the blood stream and conversion to a less toxic compound called urea. As the body eliminates urea through the kidneys, the horse’s greater frequency and amount of urination increases its water requirements, and more electrolytes can be lost.

The increased urination will also cause an increase in-barn ammonia. Like a vicious circle, stall bacteria will convert urea back into ammonia, which when inhaled, will irritate the airways of horses and humans, which can cause respiratory infections. If you can smell ammonia in the barn, it is far above the toxic levels.

In the summer, excess protein can contribute to heat stress. When food is digested heat is released, called the heat of digestion or heat increment. Certain nutrients release more heat than others and protein is one of them, even more than fat. Less heat stress will occur if horses are fed high-fat low-protein concentrates.

What Protein Doesn’t Do

Growing horses can suffer from numerous bone disorders, which are collectively called Developmental Orthopedic Disease (DOD). Many breeders and veterinarians have inappropriately blamed protein for these bone disorders. Good research, however, has proven that higher protein rations are not the cause of DOD.

The best way to limit DOD is through genetic selection, good management and feeding balanced rations to foals and broodmares. Since bone is 20 percent protein and mare’s milk is high in protein, foals and broodmares need adequate levels of high-quality proteins that are balanced with adequate amino acids, minerals and vitamins. These rations should be fed only to sustain a consistent growth rate. Even the best rations can be overfed and contribute to DOD by causing overly rapid growth.

In summary, protein is a critical nutrient, but it needs to be managed properly. In growing horses and lactating mares use higher protein rations with added amino acids. The working horse generally does not need more than 10 to 12 percent protein, and even less if alfalfa is being fed. By understanding and employing these principles, you can effectively feed the right amount of protein, thereby minimizing complications and costs.